1. Field of the Invention
The present invention relates to a communication device, a communication method and a communication system.
2. Description of the Related Art
Recently, a variety of devices such as a computer such as a notebook personal computer (PC) and a television receiver become multifunctional more and more, and a device having a function of wireless communication with another device has been widely used. Herein, the wireless communication between the above-described devices is performed by using a carrier wave (electromagnetic wave) having a predetermined frequency of 5 GHz and the like, for example.
On the other hand, technology to make a communication speed of the wireless communication higher by using a higher frequency carrier wave referred to as a millimeter wave is recently developed. Herein, the millimeter wave means the carrier wave of which wavelength is 10 mm to 1 mm and frequency is 30 GHz to 300 GHz, for example. Therefore, when using the millimeter wave such as the carrier wave of 60 GHz in the communication, for example, channel allocation in units of GHz is possible, so that the communication speed may be made higher than when using the carrier wave of 5 GHz in the communication.
In general, the millimeter wave such as the carrier wave of 60 GHz has characteristics in which straightness is stronger and attenuation associated with reflection is larger than those of the carrier wave of 5 GHz. Therefore, the communication using the millimeter wave such as the carrier wave of 60 GHz is performed by using mainly a direct wave and a reflected wave with about one reflection. Further, the millimeter such as the carrier wave of 60 GHz has characteristics in which free-space propagation loss is larger than that of the carrier wave of 5 GHz. Therefore, in general, the communication using the millimeter wave has a communication distance shorter than that of the communication using the carrier wave of 5 GHz.
In such a circumstance, technology to perform the communication by allowing the carrier wave to have the directionality is developed. There is Japanese Patent Application Laid-Open No. 2008-252240, for example, as the technology to switch the directionality of an antenna based on a communication target and a type of transmitted data.